In the operating facilities or plants found in the petrochemical and power industry, plant operators must have the ability to remotely control the operation of valves that are located throughout the plant from a main operating control room, from remote fixed control panels or from other locations remote from the locations of the valves. To accomplish this, some remotely controlled or remotely actuated valves are provided with pneumatic actuators that use a pressurized gas, such as pressurized air, as the energy source or the motive force to selectively position the valve in its open position, in its closed position or at some intermediate position.
The pneumatic actuator is typically a separate component that is attached or secured to the valve body and valve stem in such a fashion that the actuating mechanism will cause the valve stem to operate (e.g., causes valve stem to rotate) so as to cause the valve to change its position (i.e., cause the valve disc, plug or ball to stroke or move). In addition, it is common for the valve actuator to be provided with limit switches to sense the open/closed position of the valve as well as to interlock the valve actuator with other functions, as required, when the valve is in the open or closed position.
However, for these actuators the additional devices associated therewith such as the limit switches and the solenoid valve are individually constructed and each are separately mounted to the actuator. As such, special brackets must be designed and manufactured to secure each component to the actuator body. Additionally, the actuator must be designed with provisions or additional features so the brackets and components remain safely and properly secured to the actuator during the specified service conditions.
In addition to the mounting requirements, for on-site installation of these pneumatically actuated valves, the wiring providing power and control signals must be run to each separate device and an electrical termination made to each device. Further, there is typically, an electrical conduit or a flexible conduit and an associated connection for each electrical device mounted to the actuator particularly when there is a water or explosion proof design requirement imposed. Thus, the need for conduit and flexible connections for each electrical device, as well as the widely spaced wiring, makes installation of the pneumatic actuator expensive as well as creating a congestion of wiring and conduits proximate or about each pneumatic actuator.
The congested wiring, as well as the multiple conduit connections, makes maintenance of the pneumatic actuator and the related valve time consuming and expensive. For example, to remove a valve or its actuator each and every conduit connection and each and every electrical termination must be broken and the wiring and conduit/flexible conduit moved out of the way. Alternatively, the devices or components may be detached or disconnected from the actuator and left hanging from the conduit or wires while the actuator and/or valve is being removed/repaired.
Since the additional components (e.g., limit switches) are externally mounted to the actuator, each individual component must have a housing designed to meet the environmental or service conditions specified for the actuator. For example, if there was an explosion proof design requirement, each limit switch and solenoid valve mounted to the actuator would have to be constructed and designed to be explosion proof. As such, externally mounted components are generally more expensive because each component has to meet the rigorous design requirements of the actuator. In addition, this increases maintenance time and expense because these capabilities need to be maintained for each component (e.g., maintain explosion proof capability of each component housing). Generally components that are externally mounted to the actuator are also susceptible to damage, for example during installation or during maintenance activities.
There is, therefore, a need for a pneumatic actuator and an actuator controlling device that simplifies making electrical terminations and gas/air piping connections, which reduces the number of electrical conduits and which makes installation, operation and maintenance of the valve and actuator less expensive than for known pneumatic actuators. There is also a need for an actuator controlling device that simply and inexpensively can satisfy water and/or explosion proof design requirements as well as being a controlling device that can be simply and easily used for all size pneumatic actuators.